(1) Field of the Invention
The present invention relates to a bearing device of a crankshaft, and more particularly to a bearing device which includes a journal part of a crankshaft, a main bearing which rotatably supports the journal part, and a cylinder block and a bearing cap which hold the main bearing.
(2) Description of Related Art
A crankshaft of an internal combustion engine is supported at its journal part, through a main bearing constituted of a pair of half bearings, under a cylinder block of the internal combustion engine. To lubricate this main bearing, lubricating oil discharged by an oil pump is fed through an oil gallery formed inside a wall of the cylinder block and a through-hole formed in a wall of the main bearing, into a lubricating oil groove which is formed along an inner circumferential surface of the main bearing.
The crankshaft is formed with a first lubricating oil passage penetrating the journal part in the diametrical direction, and the first lubricating oil passage communicates through openings at its both ends with a circumferential oil groove of the main bearing. A second lubricating oil passage branching off from the first lubricating oil passage is formed so as to pass through a crankarm part, and the second lubricating oil passage communicates with a third lubricating oil passage formed to penetrate a crankpin in the diametrical direction. Thus, the lubricating oil fed into the lubricating oil groove of the main bearing passes through the first lubricating oil passage, the second lubricating oil passage, and the third lubricating oil passage, and thereafter is fed through an opening (a lubricating oil outlet formed in an outer circumferential surface of the crankpin) at an end part of the third lubricating oil passage, onto sliding surface between the crankpin and a connecting rod bearing.
In recent years, the oil pump for supplying lubricating oil has been reduced in size with the aim of lowering the fuel consumption of the internal combustion engine. In response to this trend, a main bearing has been proposed, wherein at least one of the pair of half bearings constituting the main bearing includes: an oil hole for introducing lubricating oil which penetrates a bearing wall plate; an oil distribution groove which extends in a circumferential direction in an inner circumferential surface and communicates with the oil hole; and a collection groove which extends in the circumferential direction to collect the lubricating oil on the inner circumferential surface of the half bearing without communicating with the oil distribution groove (e.g., see FIG. 2 of International Publication No. WO 2012/123213).
In this main bearing of International Publication No. WO 2012/123213, since the lubricating oil supplied from the oil gallery inside the cylinder block to the main bearing flows only into the oil distribution groove and does not flow into the collection groove, the amount of oil supplied to the main bearing can be reduced. That is, making the oil flow to the connecting rod bearing through the first lubricating oil passage, the second lubricating oil passage, and the third lubricating oil passage requires the lubricating oil inside the oil distribution groove to be at a high pressure. The flow rate of the lubricating oil to be supplied can be lowered by reducing the volume of the oil distribution groove as is shown in International Publication No. WO 2012/123213.
A negative pressure is generated in the collection groove of the main bearing of International Publication No. WO 2012/123213, since the collection groove is a closed space without the oil hole which penetrates the bearing wall plate to introduce the lubricating oil. This creates a suctioning effect due to the negative pressure, which causes the surrounding lubricating oil to be suctioned. As the suctioned lubricating oil is again supplied onto the inner circumferential surface, the amount of lubricating oil supplied to the main bearing can be reduced. International Publication No. WO 2012/123213 achieves the reduction in size of the oil pump by means of the effect described above.